1. Field of the Invention
The present invention relates to reactive compositions containing a blocked polyisocyanate component and an isocyanate-reactive component having primary amino groups and to their use for the production of coatings, adhesives, sealants, embedding compounds and molded articles.
2. Description of the Prior Art
A large number of reactive systems based on blocked polyisocyanates and polyamines are known. DE-A 1,644,813 describes the production of coating compositions based on ketoxime-blocked polyisocyanates and organic polyamines. These systems cure extremely slowly at room temperature and generally require temperatures above 120.degree. C. to cure, which is disadvantageous for two reasons. One, the thermal treatment is often not possible and, two, the systems tend to form bubbles during thermal treatment such that they can only be applied in thin layers.
DE-A 2,131,299 describes mixtures which can be hardened under the effect of heat and contain a polyisocyanate component having caprolactam-blocked isocyanate groups and cycloaliphatic polyamines. These compositions have good storage stability and are suitable for producing thick coatings with good mechanical properties. However, a disadvantage of these systems is the high temperature of about 160.degree. C. which is required for curing.
DE-A 3,922,767 describes heat-curable mixtures containing polyisocyanates blocked with secondary monoamines and organic polyamines. These compositions exhibit a good combination of pot life and low curing temperatures. However, elimination of the blocking agent from these systems is problematic due to the production of unpleasant odiferous compounds. In addition, the compositions of DE-A 3,922,767 cannot be used to produce coatings which harden at room temperature since the rate of hardening is too slow and, according to previous findings, cannot be catalytically accelerated.
DE-A 2,152,606 describes reactive systems based on alkylphenol-blocked polyisocyanates and polyamines that can optionally be cured in combination with epoxide resins. These reactive systems are also associated with some application-oriented disadvantages. First, the reactivity is so high that the compositions can only be applied and cured at room temperature due to the relatively short pot lives. Second, the blocking agent which is released has a comparatively low molecular weight, so that it evaporates out of the coating over time, which can lead to adhesion problems and may have a deleterious effect on the mechanical properties.
An object of the present invention is to provide reactive systems based on blocked polyisocyanates and polyamines which do not have the disadvantages of the prior art compositions.
This object may be achieved with the compositions according to the present invention which are described hereinafter.